I'm the guy that typically listens at a vol level of 7 or 8. Best audio system I have had in a car. Friends of mine have also commented on the great sound.
Based on the comments i hear, if you have bad frequency response or volume, your system is defective.
If it was mine, I would take it back to service department and have them fix it.
If they did not get it fixed with a software flash, I'd request they start replacing the main amp. If still no fix, I'd have them ohm out speaker lines and next replace the receiver.
The HK works great when it is working correct.